Technical Field
The present invention relates generally to compositions and methods for biological sample storage.
Description of the Related Art
Research in the life sciences field is based upon the analysis of biological materials and samples, such as DNA, RNA, blood, blood buffy coat cells, urine, buccal swabs, bacteria, archaeabacteria, viruses, phage, plants, algae, yeast, microorganisms, PCR products, cloned DNA, proteins, enzymes, peptides, prions, eukaryotes (e.g., protoctisca, fungi, plantae and animalia), prokaryotes, cells and tissues, germ cells (e.g., sperm and oocytes), stem cells, sorted (e.g., following immunochemical labeling) or selected (e.g., positively selected or negatively selected) cells, and of minerals or chemicals. Such samples are typically collected or obtained from appropriate sources and placed into storage and inventory for further processing and analysis. Oftentimes, transportation of samples is required, and attention is given to preserve their integrity, sterility and stability. Biological samples can be transported in a refrigerated environment using ice, dry ice or other freezing facility. However, adequate low temperatures often cannot conveniently be maintained for extended time periods such as those required for transportation between countries or continents, particularly where an energy source for the refrigeration device is lacking.
Storage containers for such samples include bottles, tubes, vials, bags, boxes, racks, multi-well dishes and multi-well plates which are typically sealed by individual screw caps or snap caps, snap or seal closures, lids, adhesive strips or tape, or multi-cap strips. The standard container format for medium to high throughput of sample storage, processing and automation of biological processes is a 96-, 384-, or 1536-well plate or array. The containers and the samples contained therein are stored at various temperatures, for example at ambient temperature or at 4° C. or at temperatures below 0° C., typically at about −20° C. or at −70° C. to −80° C. The samples that are placed and stored in the devices are most frequently contained in liquid medium or a buffer solution, and they require storage at such subzero temperatures (e.g., −20° C. or −70 to −80° C.). In some cases, samples are first dried and then stored at ambient temperature (e.g., WO 2005/113147, US 2005/0276728, US 2006/0099567), or at 4° C., at −20° C. or at −70 to −80° C.
For example, presently, nucleic acids are stored in liquid form at low temperatures. For short term storage, nucleic acids can be stored at 4° C. For long-term storage the temperature is generally lowered to −20° C. to −70° C. to prevent degradation of the genetic material, particularly in the case of genomic DNA and RNA. Nucleic acids are also stored at room temperature on solid matrices such as cellulose membranes. Both storage systems are associated with disadvantages. Storage under low temperature requires costly equipment such as cold rooms, freezers, electric generator back-up systems; such equipment can be unreliable in cases of unexpected power outage or may be difficult to use in areas without a ready source of electricity or having unreliable electric systems. The storage of nucleic acids on cellulose fibers also results in a substantial loss of material during the rehydration process, since the nucleic acid remains trapped by, and hence associated with, the cellulose fibers instead of being quantitatively recoverable. Nucleic acid dry storage on cellulose also requires the subsequent separation of the cellulose from the biological material, since the cellulose fibers otherwise contaminate the biological samples. The separation of the nucleic acids from cellulose filters requires additional handling, including steps of pipetting, transferring of the samples into new tubes or containers, and centrifugation, all of which can result in reduced recovery yields and/or increased opportunity for the introduction of unwanted contaminants and/or exposure to conditions that promote sample degradation, and which are also cost- and labor-intensive.
Proteins are presently handled primarily in liquid form as solutions (e.g., in a compatible aqueous solution containing a salt and/or buffer) or suspensions (e.g., in a saturated ammonium sulfate slurry), in cooled or frozen environments typically ranging from −20° C. to storage in liquid nitrogen (Wang et al., 2007 J. Pharm. Sci. 96(1):1-26; Wang, 1999 Inter. J. of Pharm. 185: 129-188). In some exceptions proteins may be freeze-dried, or dried at room temperature in the presence of trehalose and applied directly to an untreated surface. (Garcia de Castro et al., 2000 Appl. Environ. Microbiol. 66:4142; Manzanera et al., 2002 Appl. Environ. Microbiol. 68:4328). Proteins often degrade and/or lose activity even when stored cooled (4° C.), or frozen (−20° C. or −80° C.). The freeze-thaw stress on proteins reduces bioactivity (e.g., enzymatic activity, specific binding to a cognate ligand, etc.) especially if repeated freeze-thawing of aliquots of a protein sample is required. The consequent loss of protein activity that may be needed for biological assays typically requires the readjustment of the protein concentration in order to obtain comparable assay results in successive assays, and oftentimes results in compromised reliability of experimental data generated from such samples.
Drying of proteins and nucleic acids has yet to be universally adopted by the research scientific, biomedical, biotechnology and other industrial business communities because of the lack of standard established and reliable processes, difficulties with recoveries of quantitative and functional properties, variable buffer and solvent compatibilities and tolerances, and other difficulties arising from the demands of handling nucleic acids and proteins. The same problems apply to the handling, storage, and use of other biological materials, such as viruses, phage, bacteria, cells and multicellular organisms. Dissacharides such as trehalose or lactitol, for example, have been described as additives for dry storage of protein-containing samples (e.g., U.S. Pat. No. 4,891,319; U.S. Pat. No. 5,834,254; U.S. Pat. No. 6,896,894; U.S. Pat. No. 5,876,992; U.S. Pat. No. 5,240,843; WO 90/05182; WO 91/14773), but usefulness of such compounds in the described contexts has been compromised by their serving as energy sources for undesirable microbial contaminants, by their limited stabilizing effects when used as described, by their lack of general applicability across a wide array of biological samples, and by other factors.
The highly labile nature of biological samples makes it extremely difficult to preserve their biological activity over extended time periods. While storing nucleic acids and proteins under freeze-dried conditions (e.g., as lyophilizates) can extend the storage life (shelf-life) of a sample, the subsequent loss of activity upon reconstitution in a liquid makes freeze-drying (e.g., lyophilization) a less than ideal storage technique. Moreover, drying methods cannot be used effectively for other biological materials such as those collected in large volumes, or as swabs of surfaces for biofilm collection, or for some viruses, bacteria, or multicellular organisms. For example, the ability to maintain liquid bacteria cultures under non-selective growth conditions would be particularly desirable during long term transportation, particularly in an environment that retards the growth rate and preserves the survival of the bacteria, but no such ability currently exists. Similarly, the ability to store samples stably and for extended periods in a liquid or semi-liquid environment at ambient or near-ambient temperatures (e.g., about 23° C. to 37° C.) thereby avoiding extreme temperatures (e.g., about 0° C. to −80° C.) would be highly advantageous in maintaining fully functional and intact biological samples, as these are native conditions for many biomolecules. Such capabilities are not, however, presently known.
The degradation of biological samples collected from distant places, be it a foreign country, continent, undersea or outer space, is also currently problematic, as proper analysis and testing of the samples are subsequently compromised and/or delayed. As such, presently available storage technologies for biological samples are not adequate, particularly with regard to preparation or collection of large quantities of proteins or other types of biomolecules that may not be amenable to dry storage, and/or to biological sample modalities for which it is desirable to have a storage capability for long time periods while retaining substantially constant biological activity. For example, in the case of disease outbreak or bioterrorism investigations, such an ability to preserve the integrity of biological samples could be needed, particularly if the sample is collected under extreme environmental conditions and then subjected to variable temperature conditions and/or lengthy transportation to an appropriate facility for analysis. Thus, the ability to store biological samples for extended time periods without the need for time-consuming, impractical, inconvenient and/or costly preservation methods, particularly those that require refrigeration, would be highly advantageous.
Accordingly, there is clearly a need in the art for compositions and methods for storing biological samples without dehydration for extended time periods (e.g., in excess of two weeks, three weeks, one month, six months, nine months, one year, or longer) while maintaining the biological activity, for instance, for samples collected under extreme environmental conditions (e.g., conditions including, but not limited to, extreme temperatures (e.g., sub-zero or tropical), atmospheric conditions such as increased pressure (e.g., undersea) or low gravity (e.g., outer space), UV radiation, humidity, etc., particularly over extended time periods, without complicated preparations and storage conditions. The presently disclosed embodiments address these needs and offer other related advantages.